Frequency arrangement in carrier-wave systems



Oct. 23, 1928.

1,689,026 R. A. HEISlNG FREQUENCY ARRANGEMENT IN CARRIER WE SYSTEMS Filed July 20, 1 2 2 Sheets-Sheet .1

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R. AQHEISING FREQUENCY ARRANGEMENT IN CARRIER WAVE SYSTEMS Filed July 20. 1921 2 she s-sh et 2 ATTO/M/EY Patented Get. 23, 1%28.

UNETED STATES 1,689,0 5 career orr ce.

RAYMOND A. HEISING, OF MILLBU RN, NEW JERSEY, TO ELECTBIC COMPANY, INC, OF NEW YORK, N. Y., A CORPORATION FREQUENCY ARRANGEMENT IN CARRIER-WAVE SYSTEMS.

Application filed July 20,

This invention relates to wave length arrangen'ients, particularly as applied to a system of communication between one or more ship stations and a plurality of shore stat1ons each arranged for multiplex operation.

In multiplex radio transmission, cons derations of public convenience, the equitable treatment of competitive interests, etc.. nnpose the necessity of limiting the width of the frequency band assigned to the particular type of service. The problem of mult plex simultaneous transmission with a nummuin of interference between the various channels becomes of importance since on its solution depends the maximum traffic that the system can bear.

The problem of multiplex communication between a plurality of fixed stations and a plurality of mobile stations, such as SlllPS, differs in several particulars from that of the more common case of communication between two fixed multiplex stations, whether by high frequency waves overuyires or by radio, and is inherently more difhcult on account of the greater numberof elements 1nvolved and the greater diversity of the functions of these elements. The several channels at each shore station must each be kept free from interference with the other channels, as

in the ordinary case, and in addition each of the shore stat-ions as a whole must be kept from interference with the other shore stations, so that they can independently communicate with the shipstations without interfcrenco therebetween. The space restrictions on shipboard render the problem of selectivity and discrimination against un desired waves difficult and require, in the ordinary case, the use of special receiving apparatus which introduces new difliculties. Because of the mobility of the ship stations, their relation to the several. shore stations may continually change with further resultant complication of the problem.

The various types of interference which may affect the operation of any particular communication channel. may be classified gen erally as side-tone and as cross tallc. The fornier is measured by the el lect of a transmitter Wave on the local receiving circuit corrcspomlin'gto the same twoway conversational unit. Cross tall: may be of two kinds, one of which is measured by the effect, in a circuit tuned to a particular frequency, of a current having a different frequency trans- 1921. Serial No. 488,069.

mitted from a distant station and intended for a different receiving channel. This Wlll be denominated cross talk in the same direc tion or-merely cross talk. Cross talk of a somewhat different order occurs when the transmitted wave corresponding to one conwhere the circuits at a station are adapted to simultaneously send and receive over any or all of its channels, whetherfby useofOIle or a plurality of antennae. Cross talk can be substantially eliminated by proper spacing between the frequencies associated with the receiving channels at astat-ion, supplemented by frequency selective circuits. Thevu'se'of this i'neans is shown in "a patent to Heising 1,313,488, August 19, 1919. In side-tone and cross talk in opposite directions, the interfering frequency waves originate at the same station where the interference occurs and a balancing means such as that shown in Shreeve Patent. 1,378,982, May 2st, 1921, may

.beused to preventinterference, this means being; supplemented by frequency selectivity when the transmitting and receiving circuits concerned are arranged to eliiciently transmitand receive waves of different frequencies. H

If balanced circuits are relied on to prevent side-tone interference and cross talk in opposite directions, the balancingmeans maywell be made much more effective than frequency selective circuits for the purpose of limiting interference, hence a smaller frequency difference maybe allowable between oppositely"directed channels than between channels 1n the same direction. In other words, the spacing between the transmission channels at a station (the spacing of there ceivi'n a' channels, not shown in the figures, being of course the same, in a symmetrical arrangement) is made sufficient to avoid cross talk and the oppositely directedffrquencies corresponding to each two-way communication unit are caused to dilfer by an amount in opposite directions in each conversational great.

unit may be the same, an arrangement most favorable to elimination of cross talk in opposite directions.

However, where the receiving circult is close to a neighboring transmitting circuit, as compared with the transmitting circuit at a distant station with which it is designed to co-operate, especially if the balancing means is not very effective, the side-tone and cross talk in opposite directions may become very In this case resort may be had to particular frequency arrangements in which the frequency spacing between any two oppositely directed carrierwaves exceeds the spacing necessary to avoid cross talk in the same direction.

The above explained principles which have heretofore been applied only to systems of multiplex communication between two fixed stations, are applicable with many changes and additions, as will be pointed out in the detailed description, to the more difiicult situation in which there are a plurality of multiplex fixed stations which are adapted to communicate with a plurality of mobile stations without communication between the shore stations themselves or between the ship stations themselves.

An object of the invention is to provide various wave length arrangements whereby simultaneous carrier wave communication maybe carried on over a plurality of two-way channels without interference.

A more specific object of the present invention, stated comprehensively, is to provide various wave length arrangements whereby one or more shore stations each arranged for multiplex radio operation may, one at a time or simultaneously, communicate over any or all of their channels with one or more ship stations without interference.

The factors which require consideration are primarily the necessary frequency spacing between carrier waves and the'physical distances between the stations themselves. According to the present invention, the frequencies of the carrier waves transmitted from a shore sta-' arranged to communicate at any of these transmission frequencies and accordin ly may cooperate with each of the .shore stations in turn as 1t progresses along the shore. The transmitting frequencies of a single shore staquency scale at the left.

tion may fall within a range which does not overlap that of any other shore station. will be termed the grouped arrangement. In an alternative arrangement the transmission frequencies of each shore station may be separated by a regular frequency interval which is the same for each station and the series of frequencies appertaining to the other shore stations may then be interspersed be-. tween those of one station in such manner as to cause all to fall within a frequency range which they divide into equal frequency interval s. Tlii s will be termed the staggered arrangement. V

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figs. 1 to 5 inclusive illustrate diagrammatically, various modifications of the system of the invention; Fig. 6 illustrates diagr mmatically a form of circuit adapted to be used at mobile station in the system of the invention and Fi 7 is a diagrammatic representation of the geographical relations involving the ship and shore stations of the specific stations are denoted by different numerals such as 1 to 12 inclusive and the numerical magnitude of each of these frequencies may be readily ascertained by referring to the fre- The channels corresponding to the different shore stations are distinguished by the use of different underscore lines. It should be clearly understood that the charts of these figures show merely the frequency spacing of various channels and do not indicate the relative positions of the shore stations or their positional relation to the ship stations. The transmitting channel frequencies of the ship stations are denoted by primed numerals, it being understood that for a given two-way communication from ship toshore, the shore outgoin transmission will be identified by the carri wave frequency of a particular numeral and the ship outgoing transmission (i. e., the shore incoming transmission) will be accomplished by the carrier wave frequency of the same numeral primed. When a ship is most favorably located as t radio operation with respect to a given shore station by being nearest to it, it is a umed thatit will communicate with that pa calar shore station and use the carrier wave frequencies assigned thereto. It is also assur-ied that any given frequency channel is in use a; only one ship station at a time.

'Referring to F 1, there is provided an arrangement whereby three shore stations,

This

each multiplexed for four channels, may simultaneously communicate with ship stations over all channels without interference. The figure shows that the frequencies of the carrier waves transmitted from one shore station are staggered with respect to those transmitted from either of the others. It also shows, by the frequencies corresponding to the same numerals primed, that the frequencies of the outgoing waves from any shore station are staggered with respect to those of the incoming waves at the same shore station, that is, with respect to the frequencies of the cooperating waves transmitted from the ship stat-ions. These two features, with proper spacing, insure the avoidance of interference at the shore stations. Selecting the shore station A, for example, the transmission channels have fcquencies 678,000, 714; 000, 750,000, and 786,000 cycles. The frequencies of the receiving stations corresponding thereto will, of course, h ave an equal spacing, and it will be seen by reference to the corresponding ship channels that they employ carrier waves of frequencies 708,000, 792%,000, 700,000, and 816,000 cycles.

Usually an arrangement of tie typeillustrated in Fig. 1 and designed to give just sufficient spacing to prevent cross talk in opposite directions will give more than sufficient spacing to prevent side-tone and much greaterspacing than is necessary to prevent cross talk in the same direct-ion. For example, as illustrated in Fig. 1, there is a spacing for prevention of cross talk in opposite directions of (3,000 cycles between a receiving frequency and the closest transn'iitting fre quency at the same station. There is a spacing of 30,000 cycles, which is more than snfiicient to prevent side tone, between two oppositely directed channels which together serve for two-way communication. There is a spacing of 36,000 cycles, which is much more than sufficient to prevent cross talk in the same direction, between the carrier frequency of the received wave and the nearest received carrier frequency at the same station.

As regards the effect on the receiving circuits of station A, of two-way transmissions from the remaining shore stations to the ship stations communicating therewith, there is a spacing, for the prevention of interference, of (3,000 cycles between any recelving frequency and the nearest carrier frequency transn .itted from another shore station in the system. This type of interference is not strictly in the nature of crosstalk in the same direction, because there is no normal communication between the shore stations. It partakes more of the nature of crosstalk in opposite directions, dltfering fronrthe conventional form in that the interfering wave comes from a different, noncoinmnnicating, station, instead of from the same station.

Each ship station is intended to communicate with the nearest shore station, and in the practical case the spacing between shore stations is great-as compared with the distances over which the radio communication is being carried. This frequency spacing, viz, 6,000 cycles, may therefore be suflicient, even though much greater frequency spacing may be required between channels associated with the same station. There is a corresponding,

frequency separation of at leastl2,000 cycles between such shore station receiving frequencies and the nearest transmitting frequency employed at a ship station designed to communicate with a different shore stw.

tion. There is therefore enough separation, when aided by the different distances separating a certain ship station from the communieating and non-communicating shore stations, to prevent crosstalk in the same direction due to such transmissions. The frequency considerations apply with equal effect to interference at the ship stations.

A geographical layout in which it is assumed that the frequency allocation is that a compensation for a condition of frequency I spacing which under other circumstances would be too small, by the expedient of using a greater geographical spacing between the stations which, under such other circumstances, would tend to interfere, than between the connnunicating stations. The overall re-' suit is a greater concentration of channels in a given totalv frequency range than would otherwise be possible. I multipl x shore station is indicated by two blocks representing respectively the transmitting and receiving terminus. The arrows on the broken lines connecting the symbolic ships at the right with these termini indicate the presumed directions of transmission. The labeis attached to these lines indicate the corresponding frequencies, consistently with the frequency allocation of Fig. 1.

The foregoing discussion does not presuppose any particular type of radio tran and reception system. For example, a system involving an antenna transmit-receive switch might be employed.

Another system which is now well known makes use of high frequency oscillations at the receiver which are combined with incoming waves of considerably different frequency to. produce difierence or intermediate frel'n the figure each quency'waves which are modified in the same ,manner as the incoming waves.

made to the U. S. patent to Osborne 1,361,487,

December 7, 1920. The auxiliary source 0 may be employed as the primary energy source for the related transmitting circuit at the same station by the use of the additional circuits shown near the top of the figure, by means of which low frequency signals originating in line 2 may be transmitted over line 3 to device M in which the high frequency waves from source'O are modulated by the signal waves. The resultant wave may be transmitted, after an'iplificatitm by amplifier A, by antenna AN,. In order that the oscillator may serve a dual function as an auxiliary energy source for the re circuit and primary energy source for the transmitting circuit, the switch 1 may be closed. In some cases, oscillations generated by source 0 may be radiated directly to the receiving antenna AN by the transmitting antenna, switch 1 being open. The artificial network N, with associated circuits, is used in well known manner to conjugately connect the transmitting and receiving circuits to the common low frequency line 2. For purposes of identification, the method of operation in which the carrier wave used for transmission is combined with the mcoming carrier wave to produce the modified intermediate frequency will be hereinafter denominated modified intermediate frequency system.

7 Systems like that shown in Fig. 6, particularly the modified form, are especially adapted to ship working and in the followin discussion of the frequency arrangements as affected by these specific types of systems, reference will particularly be had thereto, although it is to be understood that. except for effects introduced on account of the mo-. bility of the ship stations, the 00116111310118 will. apply equally to ship or shore working. As indicating the nature of the interference phenomena introduced by these specific types and the differences therebetween, it is to be noted that in the modified intermediate frequency system, the intermediate frequency is normally derived from the interaction of the transmitted and received frequencies at a station, but may be derived from the interaction of other frequencies associated of the operator and maybe made different from any intermediate frequency derivable II'OIU the interaction of any two of the transmitted wave frequencies in the systen'n'although the system is still subject, to some extent, to undesirable interference effects of the kind ust d scribed. Except for this qualification, the conditions are essentially similar for the two types. For convenience, the modified intermediate frequency system will be assumed in the following description:

Considering ship station 6, for example, which transmits at 768,000 cycles and receives at 788,000 cycles, an intermediate frequency of 30,000 cycles results. The same interme diate frequency tends to result from reception of the undesired frequency from channel 11 of shore station B. Tuning of the ship station antenna is partly relied onto eliminate this undesired frequency wave, and if the intermediate frequency is sufficiently great will pern'iit response to the desired wave without response to the undesired wave. Moreover, the interfering wave comes from a different land station, and accordingly tuning will be assisted by distance, since a ship station normally communicates with the nearest shore station. Other combinations of frequencies which would give the same intermediate frequencies, such as those associated with channels 7, 7 and 10, 5 are even less favorably related to the channel 6, and can easily be discriminated against. Combinations giving intern'iediate frequencies differ-- ent from 30,000 are avoided by intermediate frequency selection.

In the system of Fig. 1, as in the others to be described, a ship station may communicate with another ship station by temporarily assuming a channel of a. shore station. If in the system of Fig. lone of the three shore sta-' tions were to be dispensed with, the carrier frequencies which had been assigned to it could. be conveniently used for ship-to-ship comn'iunication.

It is obvious that the underlying principles characterizing the operation of the system as described may be employed in other fre-- quency arrangements, and the number of channels and their frequencies may differ greatly from those shown.

Fig. 2 shows a system similar to that of Fig. 1, but adaptable to use with two shore stations. The frequency difference available for prevention of cross talk in opposite directions is the same as in Fig. 1 and on account of the smaller total number of channels used the arrangement permits a smaller frequency inill) lit)

terval between transmitting channels at a station, and also a smaller intermediate frequency, which intervals are, nevertheless sufficient in the usual case.

Fig. 8 illustrates a case suggested above in which greater separation of frequencies is required for prevention of side tone or cross talk in opposite directions than is offered by the staggered arrangement. Since, even in the staggered arrangement, the frequency difference between oppositely directed channels of a two-way unit may be made as great as desired, and greater than the separation between transmitting channels of a station, the decision to use the grouped arrangen'ient illustrated would, in a practical case, be de termined by the conditions affecting cross talk in opposite directions. By the arrangement of Fig. 3, the spacing between frequencies at each station may be as low as that required for this limiting factor, that is there must be sufficient selectivity to avoid cross talk. It is apparent that with an equal number of channels, the economy of frequency space with the present arrangement is comparable with that of the frequency arrangement of Figs. 1 and 2, although the intermediate frequency for duplex operation of the shore stations is greater. It is charac teristic of this arrangement, as of the others, that for the purpose of avoiding interference,

selectivity of the ship antenna is aided bydistance. Moreover, with this arrangement, there are no interfering shore station frequencies which can react with aparticular ship frequency to produce the intermediate frequency normally produced at that ship station. Hence the type of interference at a ship station resulting from the use of the modified intermediate frequency system in an arrangement like that of Fig. 1, is not present. As in the cases of the other arrangements considered, the alternative methods of receiving may be used. 7

7 Figs. 4 and 5 show arrangements illustrating the opposite extreme, in which the frequencies of oppositely directed channels are the same. The shore station circuits, therefore, require excellent balance in order to prevent side-tone. Except for the conditions affecting side-tone interference, these arrangements are quite similar to those of Figs. 2 and 3. That of Fig. 4 will be used where it is more important to avoid interference be tween shore stations; that of Fig. 5,.when it is more important to avoid either cross talk in the same or opposite directions at a given shore station. The modified intermediate frequency method of receiving at the ship stations, obviously, cannot be used. If the other type of intermediate frequency method is used, the ship antennae may be sharply tuned to the desired frequency. If the latter method is used, in so far as the tuning may unavoidably be broad enough to adunit currents of frequencies producing an interfering intermediate frequency, the problem is essentially similar to that of arrangements 1 and 2, although with a relatively small intermediate frequency, the interfering frequencies may both originate at the same shore station and tuning would not, in this particular case, be aided by distance.

Although the'condition has been assumed, in the description, of a plurality of shore station channels with each of which there corresponds a ship station channel, it is to be understood that the system of the invention does not necessarily require as many ship stations as there are channels since a portion only of said channels may be used. at one time, and

in fact a single ship may in turn occupy each one of the channels. According to the assumed arrangement, involving the use of a plurality of ship stations each individual to a shore station channel, the conditions would be essentially the same if the several stations described as ship stations were fixed stations, either ship or shore, and accordingly the arrangements of the invention are to be understood as applying equally well to such a system. The expression intermediate frequency system or the like will frequently be used in the claims in defining a method of receiving, intended to cover both the general and modified forms, above described.

Having described various arrangements of the invention in detail, the features which are considered novel will be covered both broadly and specifically in the appended claims.

1 hat is claimed is:

1. A system of radio communication comprising a group of nulti-two-waychannel stations, a second group of two-way-channel stations, a channel of each being adapted to cooperate with a channel of one of the first mentioned stations, the distance between co operating stations being substantially less than that between any two non-cooperating stations in different groups of stations, and transmitting and receiving c'ircults at each of said stations, the frequency spacing between the receiving channels of each of the stations of the first group being substantially greater than the minimum spacing between the receiving channels of thedifferent stations of the first group. 7

2. A system of radio communication comprising a plurality of fixed stations, constituting one group, each provided with a plurality of two-way channels, a plurality of other stations, constituting another group, each having a two-way channel arranged to cooperate with an individual two-way channel of one of the stations of thefirst group, the distance between stations provided with cooperating channels being substantially less than that between any other two stations in different groups, and the frequency between the receiving channels of each of the stations of the first group being greater than the minimum frequency spacing between two oppositely directed channels belonging to different stations of the first group.

3. A system of radio communication comprising a plurality of fixed stations each provided with a plurality of two-way channels, the channels at the several stations being arranged to cooperate with other stations located at points separated from the respective cooperating fixed stations by distances which are substantially less than the distances between such fixed stations, the frequency spacing of the receiving channels at each of said fixed stations being adaquate to prevent cross talkin the same direction, the frequency spacing, including zero spacing, of cooperating channels at each of .such fixed stations being adequate to prevent side-tone and with relation to the other frequencies, being such that there is adequate separation between the nor- 7 mal receiving frequencies at each of said fixed said fixed stations, than between the receiving frequencies at the same fixed station.

4. The system of claim 3 in which the spacing of cooperating frequencies is greater than zero.

5. The system of claim 3 including a cooperating station comprising a modified intermediate frequency system at each of a plurality of said points and in which the spacing of the cooperating frequencies, with relation to the remaining frequencies, is such that the interfering frequency nearest to the desired receiving frequency at each of said cooperating stations is transmitted from a non-cooperating fixed station.

6. The system of claim 3, including at least one mobile cooperating station, each of which is adapted to sequentially occupy positions near a plurality of said points and to cooperate with a channel at that fixed station which is arranged to cooperate with a station at the point where the mobile station ispo sitioned, each of said mobile stations comprising a modified intermediate frequency system, the spacing of the cooperating frequencies, with relation to the remaining frequencies, being such that the interfering frequency nearest to the desired receiving fre quency at each of said mobile stations is transmitted from a non-cooperating station.

In witness whereof, I hereunto subscribe my name this 16th day of July, A. D., 1921. RAYMOND A. HEISING. 

